In a Next Generation WiFi (NGiFi) system, if a synchronous orthogonal frequency division multiple access (OFDMA) technology with centralized scheduling is used, because multiple NGiFi systems run on a non-licensed frequency band, exclusion is not ensured. Therefore, when multiple NGiFi systems that do not belong to a same type coexist and the multiple NGiFi systems are not synchronized, a problem of cross timeslot interference occurs with the coexistence of the multiple NGiFi systems, that is, upstream transmission of one of the NGiFi systems interferes with downstream reception of another NGiFi system, or downstream transmission of one of the NGiFi systems interferes with upstream reception of another NGiFi system, causing a severe reduction in the total system throughput.